Liquid development utilizing a curvilinear development electrode

ABSTRACT

Images are formed by transporting a photoconductive sheet member bearing an electrostatic latent image on its recording surface through or into contact with a liquid developer along a conductive arcuate surface provided with one or more apertures through which the liquid developer is applied to the recording surface.

United States Patent Sato et al.

[54] LIQUID DEVELOPMENT UTILIZING A CURVILINEAR DEVELOPMENT ELECTRODE [72] Inventors: Masamichi Sato; Yasuo Tamai; Seiii Matsumoto, all of Asaki-shi, Saitama-ken; Satoru Honjo, Suginami-ku, Tokyo, all of Japan [73] Assignee: Xerox Corporation, Rochester, NY. [22] Filed: Aug. 19, 1968 [21 Appl. No: 753,485

[30] Foreign Application Priority Data Aug. 24, 1967 Japan ..42/54379 [56] References Cited UNITED STATES PATENTS Levene ..117/37 X 1 Feb. 15, 1972 3,196,832 7/1965 Zin ..118/637 3,202,526 8/ 1965 Ostensen ..1 17/37 3,272,176 9/1966 Saydlowskr 1 18/419 X 3,245,330 4/1966 Okishima ..95/l.7 3,345,926 10/1967 Tiger et al..... 117/37 X 3,359,945 12/1967 Hastings et al 1 18/637 3,368,526 2/1968 Matsumoto et al.. ..117/37 3,406,655 10/1968 Limberger ..1 18/637 X 3,407,786 10/1968 Beyer et al ..117/37 X 3,442,254 5/1969 Akiyama et al. 17/37 X 3,496,012 2/1970 Biorseth ..1 18/419 Primary Examiner-William D. Martin Assistant Examiner-Edward J. Cabic Attorney-James J. Ralabate, Peter H. Kondo and Albert A Mahassel 57 ABSTRACT 4 Claims, 2 Drawing Figures PAIENTEUFEB 15 I972 3.642.515

INVENTORS MASAMICHI SATO YASUO TAMAI SEIJI MATSUMOTO BY SATORU HONJO ATTO.RNEY

LIQUID DEVELOPMENT UTILIZING A CURVILINEAR DEVELOPMENT ELECTRODE BACKGROUND OF THE INVENTION electrostatic charge on a photoconductive insulating layer comprising zinc oxide powder and a resinous binder carried on a conductive paper substrate, exposing the layer to a lightand-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a charged toner which is dispersed in an insulating liquid. The charged toner may be suitably colored and may have a polarity of charge identical or opposite to that of the latent image to be developed. If the polarity of charge of the toner is identical to that of the latent image, reversal development will occur whereas a toner having a charge opposite to that of the latent image will be attracted to the latent image.

A development electrode is normally utilized in liquid development systems to improve image resolution and toner density. When an electrostatic latent image is developed without a development electrode, toner deposition is determined by the distribution of the electrostatic field emanating from the latent image and not by the distribution of charge density. In other words, the intensity of the electrostatic field is greatest at the edge of an electrostatic latent image and decreases rapidly towards the center of the image. Hence, heavy deposition of toner occurs in the high intensity field areas at the edge of the charged images, whereas very little toner is attracted to the center of the images. This phenomenon is referred to in the art as edge-effect." Development electrodes positioned close to the imaging surface of a photoconductive recording member will eliminate the edge-effect.

Although many advantages are derived from the use of development electrodes, difficulties are encountered because the development electrode must be positioned very close to the imaging surface. Prolonged developing times are required to achieve acceptable image density when development electrodes are utilized because the close spacing interferes with the supplying of toner material to the imaging surface. Further, the latent or developed images will be destroyed if the imaging surface accidentally contacts the development electrode during development. Also, uniform spacing between the photoreceptor surface and the development electrode is difficult to maintain in systems utilizing photoreceptors in flexible sheet form. Thus, there is a continuing need for an improved imaging system.

SUMMARY OF THE INVENTION It is therefore, an object of this invention to provide an imaging system overcoming the above noted deficiencies.

It is another object of this invention to provide an imaging technique which improves electrophotographic image quality.

It is a further object of this invention to provide an imaging technique which forms images with great rapidity.

It is still another object of this invention to provide an imaging technique which produces improved solid area images.

It is another object of this invention to provide an imaging technique superior to those of known techniques.

The above objects and other are accomplished by providing an imaging system in which a photoconductive sheet member bearing an electrostatic latent image on its recording surface is transported through or brought into contact with a liquid developer along a conductive arcuate surface provided with one or more apertures through which the liquid developer is supplied to the recording surface.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of the improved electrostatographic imaging system of this invention will become even further apparent upon consideration of the following disclosure of the invention, particularly when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic sectional view of an electrophotographic imaging apparatus employing an embodiment of the development electrode and liquid developer supply means of this invention.

FIG. 2 is a schematic sectional view of an alternative form of the apparatus shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, reference character 1 designates an electrophotographic recording sheet bearing an electrostatic latent image on a recording surface. The electrophotographic recording sheet 1 is delivered into a developer container 15 by means of a pair of drive rollers 11 and 12, one or both of which are driven by suitable means, not shown, in the direction indicated by the arrows. As the electrophotographic recording sheet 1 with its recording surface facing the developer container 15 is transported adjacent the arcuate, conductive inner surface 16 of developer container 15, a conventional liquid developer comprising toner particles suspended in an insulating liquid is supplied through slots 17, 18 and 19. The slots 17, 18 and 19 extend across substantially the entire width of the recording sheet 1 and are positioned substantially perpendicular to the path of travel of the electrophotographic recording sheet 1. If the electrophotographic recording sheet 1 is fed along the conductive bottom 16 of the container 15 in the absence of any developer fluid flowing through slots 17, 18 and 19, the recording surface of the electrophotographic recording sheet 1 will contact the conductive bottom 16 of developer container 15 thereby causing the destruction of both the electrostatic latent image and any developed images. In addition, any stagnant liquid developer located in the space between the electrophotographic recording sheet 1 and the conductive bottom 16 will be rapidly depleted of toner material thereby inhibiting the formation of high density images. When the liquid developer is supplied to the interior of developer container 15 through slots 17, 18 and 19 by suitable means such as a pump, not shown, the developerflow rate may be regulated by conventional flow regulators such as valves to achieve a state of equilibrium whereby the recording surface of electrophotographic recording sheet 1 is maintained a short distance away from the conductive bottom 16 of the developer container 15. Thus, the flowing developer supplied through slots 17, 18 and 19 prevents the recording surface of electrophotographic recording sheet 1 from contacting the conductive bottom 16 and also replenishes the developer material located adjacent the recording surface. Thus, the imaging system of this invention provides images free of the edge effect and characterized by high density. Images recording sheet 2 is withdrawn from developer container 15 by means of drive rollers 13 and 14.

Obviously, the number and location of apertures in the conductive arcuate bottom can be altered as long as the spacing and development rate requirements of this invention are met. Also, considerable latitude exists in the degree of curvature of the arcuate curvilinear bottom. The degree of curvature selected will depend upon other variables such as the relative locations of the apertures, the liquid developer flow rate, the stiffness and length of the recording sheet, the location of the drive means and the like. Although not illustrated in the drawings, it should be apparent that other modifications can be made such as the use of a suitable backing member mounted in the developer container to support the rear surface of the recording sheet as it passes through the container. As is well known in the electrode development art, the electrode may be either electrically connected to a suitable reference potential or to ground for the establishment of an electric field adjacent the recording surface. The conductive backing of the recording sheet may be connected to ground through the use of conductive drive rollers such as the rollers 12 and 13 illustrated in FIG. 1.

in FIG. 2, another embodiment of the invention is shown wherein liquid developer material is prevented from contacting the rear surface of an electrophotographic recording sheet la thereby avoiding discoloration of the rear surface by absorption of developers. Total immersion of the electrophotographic recording sheet In is prevented by regulating the flow rate of the liquid developer through slots 17a, 18a and 19a, by means of conventional flow regulators, not shown, so that the flow of developer liquid through each slot is initiated immediately prior to or when the electrophotographic recording sheet passes over the slot. By controlling the flow rate of the liquid developer and by providing drain outlets suitably located in or adjacent to the conductive bottom 16a of developer container a, flooding of the rear surface of the electrophotographic recording sheet la can be avoided during development. Electrophotographic recording sheet la is depicted in FIG. 1 as a sheet. However, a continuous web may be substituted therefore. Thus, the expression sheet" as employed herein is intended to include webs.

Although slots extending perpendicular to the path of electrophotographic sheet travel are illustrated in the drawings, it is obvious that other types of apertures can be suitably located along the conductive curvilinear bottom of the liquid developer container to supply the required quantity of flowing liquid developer. For example, the required quantity ofliquid developer may be supplied through a plurality of staggered nozzles positioned along the conductive bottom of the developer container. A sufficient number of nozzles should be employed to span substantially the entire width of the recording sheet.

The imaging technique of this invention, as may be clearly understood from the foregoing description, provides high quality, dense images free of any edge effect. These improved images are realized by maintaining a close spacing between a development electrode and a recording surface without encountering difficulties with developer depletion or undesirable contact between the recording surface and the development electrode. Further, the circulation of developer liquid through the development system inhibits the agglomeration of toner particles, thereby enhancing image resolution.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, other modifications and ramifications of the present invention will appear to those skilled in the art upon a reading of the disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A method of forming a toner image comprising providing a flexible electrophotographic imaging sheet having an upwardly facing surface and a downwardly facing recording surface bearing an electrostatic latent image, transporting said downwardly facing recording surface in an arcuate path adjacent and substantially concentric to an upwardly facing, downwardly bowing, arcuate surface of a curvilinear development electrode containing at least one aperture, supplying sufflcient liquid developer material comprising toner particles suspended in an insulating carrier fluid through said aperture to contact and maintain the portion of said recording surface in contact with said liquid developer out of contact from said upwardly facing, downwardly bowing, arcuate surface and maintaining free of contact with solid members the portion of said upwardly facing surface of said imaging sheet immediately opposite said portion of said recording surface in contact with said liquid developer whereby at least a portion of said toner particles deposit on said recording surfacein image configuration.

2. A method according to claim 1 including immersing said imaging sheet in said liquid developer as said imaging sheet is transported along said arcuate path.

A method according to claim 1 including maintaining substantially all of said liquid developer material below said upwardly facing surface of said imaging sheet whereby said upwardly facing surface of said imaging sheet remains free of liquid developer material as said imaging sheet is transported through said arcuate path.

4. A method according to claim 1 including contacting said recording surface with liquid developer supplied through at least one narrow slot in said curvilinear development electrode positioned opposite said downwardly facing recording surface and spanning substantially the entire width of said recording surface. 

2. A method according to claim 1 including immersing said imaging sheet in said liquid developer as said imaging sheet is transported along said arcuate path.
 3. A method according to claim 1 including maintaining substantially all of said liquid developer material below said upwardly facing surface of said imaging sheet whereby said upwardly facing surface of said imaging sheet remains free of liquid developer material as said imaging sheet is transported through said arcuate path.
 4. A method according to claim 1 including contacting said recording surface with liquid developer supplied through at least one narrow slot in said curvilinear development electrode positioned opposite said downwardly facing recording surface and spanning substantially the entire width of said recording surface. 